This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-287716, filed Sep. 21, 2000; and No. 2001-012257, filed Jan. 19, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a semiconductor processing apparatus and to a method of manufacturing the semiconductor device, and in particular, to a semiconductor processing apparatus and to a method of manufacturing the semiconductor device, wherein a process gas is introduced into a vacuum chamber for treating a substrate to be processed (hereinafter referred to as a substrate).
2. Description of the Related Art
The treatment of a substrate has been conducted according to the following procedures in a semiconductor processing apparatus, specifically a plasma etching apparatus or a plasma CVD apparatus, which is designed to generate plasma for decomposing a process gas employed for treating the substrate.
First of all, a process gas is introduced into a process chamber of a vacuum state. Then, by the application of high-frequency, a plasma is caused to generate in the process chamber, thereby decomposing and exciting the process gas. As a result, the substrate is treated by the highly reactive active species thus generated. It should be noted however that not all of the process gas that has been introduced into the vacuum process chamber is consumed by the reaction thereof with the substrate in the semiconductor processing apparatus. Rather, most of the process gas that has been introduced into the vacuum process chamber is not utilized but permitted to go out of the system by a vacuum pump.
Under the circumstances, it is urgently desired to improve the utilization efficiency of the process gas so as to reduce the cost for the process gas in the manufacturing cost involved in this etching or CVD process.
Meanwhile, various kinds of PFC (Perfluoro Carbon) gas having a high GWP (Global Warming Potential) are now used in large amounts as the process gas or as the cleaning gas of the apparatus in the etching process or CVD process. It is urgently imposed on the manufacturers of semiconductor device to take measures to reduce the quantity of the PFC gas to be released into air atmosphere for the purpose of suppressing the warming of the earth. As a matter of fact however, it has been considered very difficult at this moment to find out an alternate gas which is low in GWP, excellent in safety, and moreover, capable of exhibiting a desirable performance which is at least comparable to that of the PFC gas. Under the circumstances, it is very important subject matter at present to enhance the utilization efficiency of the process gas which is available now, thereby reducing the quantity of the process gas to be used.
With a view to overcome this problem, an apparatus as explained below has been proposed (Japanese Patent Unexamined Publication (Kokai) No. H9-251981). According to this prior art, a plasma etching apparatus or a plasma CVD apparatus which is designed to treat a substrate in a vacuum process chamber is constructed such that a circulation piping is provided between a exhaust side piping and the process chamber so as to allow a portion of exhausted gas to return into the process chamber, thereby making it possible to re-use the gas.
Since the process gas that has been once exhausted is recycled back to the process chamber according to this system, it would be possible to enhance the utilization efficiency of process gas and hence to save the quantity of process gas, resulting in that the quantity of PFC gas to be discharged into the atmosphere can be greatly reduced. However, this system is accompanied with several problems if it is to be actually applied to the plasma processing step in the actual production site as explained below.
One of the problems is the accumulation of deposit inside the circulation piping in a long-term running. Not only in the plasma CVD process, but also in the etching process where high-selectivity characteristics such as highly selective etching of oxide film is necessitated, a process gas to be circulated is more likely formulated so as to contain a large amount of reactive components which can be very easily adhered onto the surface of solid matter. In this case, it is assumed that most of the reactive components will adhere onto the inner wall of the process chamber, but the reactive components is allowed to adhere partially on the inner wall of the circulation piping as the process gas passes through the circulation piping. If the deposit that has been adhered onto the inner wall of the circulation piping is peeled off and allowed to flow as dust into the process chamber, the deposit may adhere onto a wafer, thus possibly deteriorating the yield of the device being treated. Therefore, according to the current practice, it is considered inevitable, for the purpose of preventing the peeled deposit from flowing as dust into the process chamber, to entirely exchange the circulation piping with a fresh one every predetermined period. It is also proposed to provide a filter in the circulation piping. However, since the provision of ordinary filter would lead to the deterioration of conductance due to the clogging of the filter, the proposal is not necessarily appropriate.
The other problem is related to the method of controlling the flow rate of circulating gas. Namely, according to the aforementioned system, the opening degree of valve for controlling the flow rate of circulating gas is required to be checked every time depending on the process conditions, which is rather troublesome.
A semiconductor processing apparatus according to one embodiment of the present invention comprises:
a process chamber treating a substrate;
a process gas feeder feeding a process gas to the process chamber;
a first vacuum pump exhausting the process chamber;
a second vacuum pump inhaling gas on an exhaust side of the first vacuum pump; and
a circulation path circulating at least a part of the process gas exhausted from the process chamber via the first vacuum pump into the process chamber;
wherein the circulation path is provided with a dust trapping mechanism, the dust trapping mechanism being capable of substantially maintaining a conductance of the circulation path before and after the capture of dust.
A method of manufacturing a semiconductor device according to one embodiment of the present invention comprises:
exhausting a process chamber;
feeding a process gas to the exhausted process chamber;
applying a high-frequency power to the process gas to generate a plasma to treat a substrate;
exhausting the process gas from the process chamber;
circulating at least part of the process gas that has been exhausted from the process chamber to the process chamber;
suspending the circulation of the process gas to the process chamber; and
stopping the application of the high-frequency power subsequent to the suspension of the circulation of the process gas.
A method of manufacturing a semiconductor device according to another embodiment of the present invention comprises:
exhausting a process chamber;
feeding a process gas to the exhausted process chamber;
applying a high-frequency power to the process gas to generate a plasma for treating a substrate;
exhausting the process gas from the process chamber;
circulating at least part of the process gas that has been exhausted from the process chamber, to the process chamber via a circulation path, a deposit from the process gas being allowed to deposit inside a passage of the exhausted process gas;
accumulating the time taken to treat the substrate while circulating the process gas; and
circulating an active gas as the time accumulated reaches a provided period, to allow the active gas to react with the deposit formed inside the passage of the exhausted process gas to remove the deposit.
A method of manufacturing a semiconductor device according to another embodiment of the present invention comprises:
exhausting a process chamber;
feeding a process gas to the exhausted process chamber;
applying a high-frequency power to the process gas to generate a plasma for treating a substrate;
exhausting the process gas from the process chamber;
circulating at least part of the process gas that has been exhausted from the process chamber, to the process chamber via a circulation path, a deposit from the process gas being allowed to deposit inside a passage of the exhausted process gas;
monitoring a thickness of the deposit thus deposited; and
circulating an active gas as being monitored that the thickness of the deposit reaches a provided thickness to allow the active gas to react with the deposit deposited inside the passage of the exhausted process gas to remove the deposit.